SOME EFFECTS OF PENTOBARBITAL AND STRYCHNINE ON TRANSMISSION THROUGH THE VENTROBASAL COMPLEX OF THE CAT THALAMUS

¹ Department of Pharmacology, The University of Rochester, Rochester, New York

The effects of pentobarbital (6.25, 12.5 and 25 mg/kg) and of strychnine (0.2 mg/kg) were studied on transmission through the ventrobasal complex (VBC) of the thalamus of unanesthetized cats which were paralyzed with gallamine and whose wounds were infiltrated with lidocaine. The medial lemniscus was stimulated, and the response was recorded in VBC or the internal capsule. Drug effects were determined on the recovery cycle at 1- to 200-msec interstimulus intervals and on the amplitude, latency and width of the response to the conditioning stimulus. Pentobarbital decreased the amplitude and increased the latency and width of the response to the conditioning stimulus. The amount of recovery increased at 1 to 4 and 80 to 110 msec and decreased at 12 to 60 msec. The magnitudes of these effects were dose-related. Strychnine in unanesthetized cats increased the amplitude of the response to the conditioning stimulus and increased the amount of recovery at interstimulus intervals greater than 8 msec. Strychnine produced two apparent peaks in the recovery cycle, one at 40 msec and the other between 100 and 200 msec. When strychnine was given to pentobarbital-anesthetized cats, it was found to be without effect. These effects on the recovery cycle are consistent with the interpretation that strychnine decreases postsynaptic inhibition in VBC of unanesthetized cats and that pentobarbital increases postsynaptic inhibition. Pentobarbital also decreases a short-latency (1- msec) inhibitory process in VBC.